Digits are Primes
Number Theory
Level
2
Find the largest two digit number whose sum and product of digits are both primes
The answer is 21.
This section requires Javascript.
You are seeing this because something didn't load right. We suggest you, (a) try
refreshing the page, (b) enabling javascript if it is disabled on your browser and,
finally, (c)
loading the
non-javascript version of this page
. We're sorry about the hassle.
1 solution
Two important things that need attention here are :-
1. number itself need not to be prime. We need to focus on digits sum and product.
2. Definition of prime:- no factor other than 1 and number itself.
So starting with 99, we need to see prime definition. If we multiply digits of a number, then their product has the multiplying digits as its factor. So we need to focus only those number which has 1 in it. So go on with 91 81 71 61 51 41 31 21 19 18 17 ......12 11 10 out of which only 21 and 12 satisfies given condition. 21>12 answer=21